1. Field of the Invention
The present invention relates generally to a BLDC (brushless direct current) motors, and more particularly, to a control circuit for BLDC motors.
2. Description of the Related Art
BLDC motors are nowadays gaining popularity in automotive, consumer, and industrial applications. They have many advantages over traditional brushed DC motors, such as higher efficiency, linear speed and torque characteristics, low acoustic noise generation, wider speed range, less maintenance, and longer operating life.
Unlike brushed DC motors being commutated by brushes, BLDC motors are electronically commutated. They are mostly controlled in three-phase configuration. Three hall sensors are embedded into the stator to detect the current rotor position and to determine which two windings will be next energized. The sequence of energizing the windings of the BLDC motors is also known as six-step commutation.
To control BLDC motors, DSP (digital signal processor) is a mostly chosen solution owing to its quick processing capability of measuring or filtering the analog signals. However, its complexity always dominates the main cost of the BLDC motor system.
Speed and torque are two key parameters for controlling a BLDC motor. In conventional arts, an inner torque control loop and an outer speed control loop are cascaded configured. The disadvantage of these arts is they are specifically designed for specified application. They fail to meet other requirements without design changes. Therefore, a BLDC control circuit with low cost and high design flexibility for wide applications is demanded by the industries.